Neuronal stimuli are transmitted by the central nervous system (CNS) through the interaction of a neurotransmitter released by a neuron, which neurotransmitter has a specific effect on a neuroreceptor of another neuron.
L-glutamic acid is considered to be the major excitatory neurotransmitter in the mammalian CNS, consequently playing a critical role in a large number of physiological processes. Glutamate-dependent stimulus receptors are divided into two main groups. The first group comprises ligand-controlled ion channels whereas the second comprises metabotropic glutamate receptors (mGluR). Metabotropic glutamate receptors are a subfamily of G-protein-coupled receptors (GPCR).
At present, eight different members of these mGluRs are known. On the basis of structural parameters such as sequence homology, the second messenger system utilized by these receptors and their different affinity to low-molecular weight compounds, these eight receptors can be divided into three groups: mGluR1 and mGluR5 belong to group I which couple to phospholipase C and their activation leads to intracellular calcium-ion mobilization. Both mGluR2 and mGluR3 belong to group II and mGluR4, mGluR6, mGluR7 and mGluR8 belong to group III, which couple to adenyl cyclase with their activation causing a reduction in second messenger cAMP and as such a dampening of the neuronal activity.
The presence of Group I mGluR antagonists has been shown to result in a reduced presynaptic release of the neurotransmitter glutamate and consequently, to decrease glutamate-mediated neuronal excitation via postsynaptic mechanisms. Since a variety of pathophysiological processes and disease states affecting the CNS are thought to be due to excessive glutamate induced excitation, group I mGluR antagonists could be therapeutically beneficial in the treatment of CNS diseases.
Therefore, group I mGluR antagonists may be administered to provide neuroprotection in acute and chronic pathological conditions such as: AIDS-related dementia, Alzheimer's disease, Creutzfeld-Jakob's syndrome, bovine spongiform encephalopathy (BSE) or other prion related infections, diseases involving mitochondrial dysfunction, diseases involving β-amyloid and/or tauopathy such as Down's syndrome, hepatic encephalopathy, Huntington's disease, motor neuron diseases such as amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), olivopontocerebellar atrophy, post-operative cognitive deficit (POCD), Parkinson's disease, vascular and frontal lobe dementia, eye injuries, eye disorders (e.g. glaucoma, retinopathy), head and spinal cord injuries/trauma, hypoglycaemia, hypoxia (e.g. perinatal), ischaemia (e.g. resulting from cardiac arrest, stroke, bypass operations or transplants), seizures/convulsions/epilepsy, glioma and other tumours, inner ear insult (e.g. in tinnitus, sound or drug-induced), L-dopa-induced and tardive dyskinesias, Wilson's disease.
Other indications in this context include a symptomatological effect on the following conditions: addiction (nicotine, alcohol, opiate, cocaine, amphetamine obesity and others), amyotrophic lateral sclerosis (ALS), anxiety and panic disorders, attention deficit hyperactivity disorder (ADHD), restless leg syndrome and hyperactive children, autism, seizures/convulsions/epilepsy, dementia (e.g. in Alzheimer's disease, Korsakoff syndrome, vascular dementia, HIV infections, Down's syndrome), depression (including that resulting from Borna virus infection) and bipolar manic-depressive disorder, drug tolerance e.g. to opioids, dyskinesia (e.g. L-Dopa-induced, tardive dyskinesia or in Huntington's disease), fragile-X syndrome, Huntington's chorea, irritable bowel syndrome (IBS), migraine, multiple sclerosis, muscle spasms, pain (chronic and acute), Parkinson's disease, post traumatic stress disorder, schizophrenia, spasticity, tinnitus, Tourette's syndrome, urinary incontinence and vomiting, Wilson's disease.